I'm constantly drinking tea at home. (I make another mug almost as soon as I've finished the first one). I hardly ever drink coffee at home nowadays (although I tend to opt for coffee when I'm 'eating out' - which usually means a local burger van!)
However in my college days I was drinking up to 30 mugs of coffee per day, often with three heaped teaspoonfuls of Nescafé in each of them. So that's the equivalent of up to 90 mugs per day. (I understand that the fatal dose for caffeine is around 130 cups per day but, apart from not sleeping very much, I didn't seem to suffer any adverse effects).
After I left college I drank less coffee but seemed to almost live on Pro-Plus caffeine tablets.
So lots of caffeine doesn't seem to have done me too much harm. (My blood pressure is a little on the high side these days, although not particularly abnormal for a sedentary guy in his mid-60s, which is partly why I've switched from coffee to tea - but I still need my caffeine fix!)